DISEASES 



DISEASES 



495 



spraying of crops like potatoes, beans, egg-plants and 

 celery, can be done with great rapidity with the cart 

 machines. 



With the annual crops the idea of cleaning up and 

 burning the rubbish should be enforced as thoroughly 

 as with the tree crops. The burn heap is a successful 

 ally of the spray pump, and with the rotation suggested, 

 growers of vegetables and vegetable fruits should hope 

 to be exempt from serious fungous attacks, except when 

 the weather is unusually favorable forthe excessive de- 

 velopment of blights and rots. 



Some of the leading fungous enemies upon the vege- 

 table fruit plants are the anthracnose (CoUetotrichum 

 Lagenarium ) and bacteriosis {Bacillus Phaseoli) of the 

 bean, both held in check by Bordeaux; the leaf-spot 

 (Ascochyta Pisi) and mildew {Erysiphe Martli) of the 

 pea; leaf-spot {Scploria Lycopersici), black-rot {Mac- 

 rosporium Tomato) and bacteriosis {Bacillus Solance- 

 arum) of the tomato; leaf-spot {Phyllosticta hortoruyn) 

 and stem-rot {Nectrla Ipomwa) of the egg-plant; and 

 anthracnose { Colletotrichtwi Lagenarium) of melons and 

 cucumbers. 



Among vegetables strictly so-called, there is the leaf- 

 blight {Cercospora ApU) and bacteriosis of celery; mil- 

 dew (P(;rortos^ora e/'/itsa) of spinach; smut \ LT roc yst is 

 Cepulce) of onions; rust {Puccinia Asparagi) of aspara- 

 gus; club-root { Pal smodiophora Brass icce) oic'Ahhs.gQ, 

 and mildew {Bremia LacUicce) of lettuce. 



The root crops have their subterranean fungous ene- 

 mies, and for these a soil treatment is necessary. For 

 the club-root of turnips and cabbage, named above, and 

 allied plants, lime is a preventive when added to the 

 soil, 35 bushels per acre; while the scab {Oospora 

 scabies) of the round potato is checked by soaking the 

 seed in a weak solution of corrosive sublimate, or by 

 flowers of sulfur added to the soil, 300 pounds per 

 acre. The same treatment is effective for onion smut 

 and the fungous diseases of the sweet potato. Use a 

 new field each year whenever possible. In short, feed 

 and care for the crops well, so that the plants will be 

 perfectly at home in the place assigned them, and then 

 use fungicides as an enlightened judgment dictates, 

 not forgetting to destroy the autumn rubbish, the win- 

 ter hiding places of the insidious germs of disease. See 

 Puugicide. 



Bacterial Diseases.— There is much damage done 

 to higher plants by infesting bacteria. These low or- 

 ganisms may flourish in leaf, stem or root, and with 

 some crops they are widespread and destructive. One 

 of the most prominent of the bacterial diseases is the 

 flre-blight of the pear, apple and quince, due to the 

 Bacillus amylovonfs, the germs of which multiply in 

 the nectar of the blooms with great rapidity, and are 

 carried from one flower to another by insects, and in 

 this way an orchard may become infected. From the 

 blossoms the disease extends downward into the 

 branches or runs in from lateral fruit-spurs and girdles 

 the limbs. The blight also enters through the tips of 

 growing branches, as in the nursery when plants are too 

 young to bear flowers. This is "twig-blight," as dis- 

 tinguished from "flower-blight," while a third form is 

 a "body-blight." where the germs attack the main 

 stem of the tree through the buds that may be found 

 there. Warm, moist weather, with frequent showers, 

 favor the spread of the disease, and with opposite con- 

 ditions the germs may die out, even when in the cam- 

 bium and protected by the bark. The germs, when they 

 live over winter in the branch, may reach the surface as 

 ooze from the blighted parts in spring and be carried 

 by insects to the flower and other buds. As yet there is 

 nothing better for a remedy than the removal of the 

 blighted twigs, cutting well below where the dead ad- 

 joins the living bark. Trees highly fertilized with ni- 

 trogenous manures are especially subject to blight and, 

 therefore, over-stimulation with manure is to be avoided. 

 and upon very rich soil an orchard may do better in sod. 



The above is a fair type of the bacterial diseases of 

 ligneous plants. Among the many upon herbs, there is 

 one that is very destructive to tomatoes, the Bacillus 

 solanacearum, which is recognized by a sudden wilting 

 of the foliage, followed by a yellow or brown color. 

 Here, again, the germs are transmitted by insects as 

 Colorado and flea beetles. One of the chief preventive 



measures, therefore, is to protect the tomatoes by insec* 

 ticides, and when any plant is diseased it should be de- 

 stroyed. Other plants allied to the tomato, as potato, 

 egg-plant, petunias and the common weeds, as James- 

 town weed, nightshade and ground cherry, are affected 

 with the same disease; and, therefore, clean culture is 

 demanded, and also a wide rotation of crops upon soil 

 liable to bear infected plants. 



A similar bacterial disease is met with in sweet corn, 

 due to Pseudomoaas iStewarti; while other species at- 

 tack sorghum and a long list of field and garden crops, 

 particularly the roots like beet, carrot, turnip and simi- 

 lar plants, as the bean, onion and celery. Sprays do not 

 seem to materially check these diseases, and the chief 

 means of combating them are through soil sanitation 

 and a judicious rotation. 



Nematodes. — There are many troubles experienced 

 by plants that are due to animals. None of these are 

 more abundant and destructive than the nematodes, 

 namely, microscopic worms, that infest various parts of 

 plants, but the roots in particular, when they cause en- 

 largements known as root-galls. As the conditions of 

 continued warmth and moisture favor these eel worms, 

 they are more frequently found in destructive numbers 

 in the plant house. Roses are particularly subject to 

 nematodes, which upon their roots cause a multitude 

 of small swellings. The same is true of violets, with 

 which they have been very serious at times. Cucumber, 

 tomato, cyclamen, coleus {see Fig. 518, p. 351), and 

 other plants are likewise attacked. 



It is thought that lime added to the soil has been bene- 

 ficial, but the most effective method of exterminating 

 these pests is by heating the soil by steam up to at least 

 180^-212° F. for one hour or more before being used in 

 the pots or benches. The nematodes are killed by freez- 

 ing, and probably on this account the number of these 

 worms in field crops is kept within bounds at the north, 

 while they are a menace to field crops at the south. In 

 greenhouse work, take care that no soil is used which 

 has not been thoroughly frozen since it bore a crop of 

 indoor stuff. 



Imperfect Nutrition.— There are doubtless many 

 ills of plants due directly to lack of proper physical con- 

 ditions. Some are overfed, others are starved, some are 



yt (: 



m 



726. Disease of Cucumber leaf (X K). 



Tlie dying margin indicates that the trouble is due to some 



interference with the food supply. 



drowned, and many perish from protracted thirst. Aside 

 from all this, plants will sicken even when the ordinary 

 conditions seem satisfactory. For some reason not 

 easily assigned, a change will coiue over the plant, the 

 activities of growth are checked or cease, and the plant 

 dies and without any cause that falls under the previous 

 heads. Some physiological defect is charged with the 

 cause, and various terms have been used to conceal the 

 manifest ignorance. The "yellows" of the peach seems 



